function changeTarget() {
        var lnks = document.getElementsByTagName('a');
        for(i=0; i<lnks.length; i++) {
                if(lnks[i].getAttribute('rel') == 'external') {
                        lnks[i].onclick = new Function('window.open(this.href); return false');
                }
        }
}
onload = changeTarget;